Background Carriage of carbapenem-resistant Enterobacteriaceae (CRE) in humans may contribute to the dissemination of CRE and impact on communities and healthcare facilities. Carbapenem-resistant Escherichia coli (CREC) is one of the major type of CRE in the human gut. Here, we describe a cross-sectional study to investigate the prevalence of CREC, and in particular the mcr-1 carrying CREC, in health volunteers in China. Methods During September to December 2016, 3859 non-duplicated stool specimens were collected from healthy volunteers who received regular physical examinees in healthcare centers located in 19 provinces across China. Enrichment culture supplemented meropenem was used to isolate CREC. Carbapenemase producing determinants and the mcr-1 gene were determined by PCR amplification and sequencing. Isolates were further analyzed by antibiotic susceptibility test, genotyping, and whole genome analysis. Findings A total of 92 non-duplicated CREC were isolated from 3859 stool specimens, among which 43 CREC are carbapenemase positive. In addition, the co-existence of bla NDM and mcr-1 was found in 14 CREC, which also showed resistance to the majority of all antimicrobial agents analyzed. The genetic background of these CREC isolates are highly diversified based on molecular typing. Furthermore, whole genome sequence indicated that NDM-5 is the predominant determinant conferring carbapenem resistance in CREC, and that NDM-5 carrying plasmids (IncX3) are very similar. Interpretation The incidence of CREC carriage in healthy people in China was small; however, the co-existence of CREC with mcr-1 is disconcerting. Therefore, pre-screening prior to admission and monitoring of patients on high-dependency wards is highly recommended to control and prevent the dissemination of CRE in hospitals. Outstanding Question The high prevalence of CREC in the healthy people should not be underestimated, as it may increase the risk of infection. This knowledge could have impact on the pre-screening and monitoring of CRE before patient administration.

The wide dissemination of New Delhi metallo-β-lactamase genes (blaNDM) has resulted in the treatment failure of most available β-lactam antibiotics, with IncX3-type blaNDM-5-carrying plasmids recognised as having spread worldwide. In China, bacteria carrying these plasmids are increasingly being detected from diverse samples, including hospitals, communities, livestock and poultry, and the environment, suggesting that IncX3 plasmids are becoming a vital vehicle for blaNDM dissemination. To elucidate the fitness cost of these plasmids on the bacterial host, we collected blaNDM-negative strains from different sources and tested their ability to acquire the blaNDM-5-harboring p3R-IncX3 plasmid. We then measured changes in antimicrobial susceptibility, growth kinetics, and biofilm formation following plasmid acquisition. Overall, 70.7% (29/41) of our Enterobacteriaceae recipients successfully acquired the blaNDM-5-harboring p3R-IncX3 plasmid. Contrary to previous plasmid burden theory, 75.9% (22/29) of the transconjugates showed little fitness cost as a result of plasmid acquisition, with 6.9% (2/29) of strains exhibiting enhanced growth compared with their respective wild-type strains. Following plasmid acquisition, all transconjugates demonstrated resistance to most β-lactams, while several strains showed enhanced biofilm formation, further complicating treatment and prevention measures. Moreover, the highly virulent Escherichia coli sequence type 131 strain that already harbored mcr-1 also demonstrated the ability to acquire the blaNDM-5-carrying p3R-IncX3 plasmid, resulting in further limited therapeutic options. This low fitness cost may partly explain the rapid global dissemination of blaNDM-5-harboring IncX3 plasmids. Our study highlights the growing threat of IncX3 plasmids in spreading blaNDM-5.

Tigecycline, the first member of glycylcycline class antibiotic, is often considered one of the effective antibiotics against multidrug-resistant (MDR) infections. However, the emergence and wide distribution of two novel plasmid-mediated tigecycline resistance genes, tet (X3) and tet (X4), pose a great threat to the clinical use of tigecycline.

A novel Gram-stain-negative, aerobic, motile bacterial strain, D13-10-4-6T, was isolated from the bark sample of Populus × euramericana. The strain could grow at 15–35°C, at pH 6–10 and in 0–4% (w/v) NaCl, and the strain tested positive for oxidase and catalase activities. The main polar lipids were phosphatidylmonomethylethanolamine, diphosphatidylglycerol, phosphatidylglycerol, and phosphatidylethanolamine. The main respiratory quinone was Q-10, and the predominant fatty acid was C18:1 ω7c. The phylogenetic analyses showed that the strain belonged to the genus Pseudogemmobacter of the family Rhodobacteraceae. The family Rhodobacteraceae is an ecologically diverse group that includes bacteria from aquatic to terrestrial ecosystems. As a consequence, the classification of the family Rhodobacteraceae is difficult, not least when the early taxonomy work relied heavily on 16S rRNA gene analysis. Recently, the taxonomic status of many members of the family has been revised based on the genome analysis; however, there are still some classification conflicts due to the lack of genome sequences and parallel publication time. In this study, phylogenetic trees based on 16S rRNA gene, gyrB gene, and 120 concatenated proteins, the average amino acid identity (AAI) and percentage of conserved proteins (POCP) have been used for the analysis of strain D13-10-4-6T and other members of 15 genera within the family to further clarify their taxonomic relationships. For the data of phylogeny, AAI, and POCP, the taxonomic proposals are (1) reclassification of Rhodobacter tardus as the type species of a novel genus, Stagnihabitans gen. nov., as Stagnihabitans tardus comb. nov.; (2) reclassification of Tabrizicola alkalilacus, Tabrizicola sediminis, Tabrizicola algicola into a novel genus, Pseudotabrizicola gen. nov., as Pseudotabrizicola alkalilacus comb. nov., Pseudotabrizicola sediminis comb. nov., Pseudotabrizicola algicola comb. nov.; (3) reclassification of Rhodobacter sediminicola into the genus Cereibacter as Cereibacter sediminicola comb. nov.; (4) reclassification of Rhodobacter flagellatus, Rhodobacter thermarum, and Xinfangfangia soli into the genus Tabrizicola as Tabrizicola flagellatus comb. nov., Tabrizicola thermarum comb. Nov., and Tabrizicola soli comb. nov.; (5) reclassification of Xinfangfangia humi into the genus Pseudogemmobacter as Pseudogemmobacter humicola comb. nov.; (6) classification of strain D13-10-4-6T as a novel species of the genus Pseudogemmobacter, for which the name P. hezensis sp. nov. is proposed, the type strain is D13-10-4-6T (= CFCC 12033T = KCTC 82215T).